The present invention relates to optical transducers (sometimes referred to as optical sensors) which utilize optical means for sensing mechanical displacements, such as movements of a body or deformation of a membrane, and converting them to electrical signals. The invention also relates to methods of making such optical transducers. The invention is particularly useful in making optical microphones for converting sound into electrical signals and is therefore described below especially with respect to this application.
Optical transducers of this type are described, for example, in U.S. Pat. Nos. 5,771,091; 5,969,838; 6,091,497; and 6,239,865, the contents of which patents are incorporated herein by reference.
Such optical transducers generally include an optical unit containing a light source, a laterally spaced light detector, an optical shield between the light source and light detector, and a displaceable member aligned with the optical window defined by the light source, light detector, and optical shield between them. The displaceable members in the optical transducers described in the above patents are generally in the form of deformable membranes, but may be physically movable members, such as in an accelerometer. Optical transducers of this type can be constructed to be very accurate for measuring very small displacements.
In general, the known optical transducers do not readily lend themselves to low-cost mass production, and therefore are relatively expense to produce. In addition, many of the known constructions are not sturdy, and therefore are not capable of withstanding rough handling.
One object of the present invention is to provide a method of producing optical transducers in a manner which permits mass production at relatively low cost. Another object of the invention is to provide a novel optical transducer of a sturdy construction which is capable of withstanding rough handling.
According to one aspect of the present invention, there is provided a method of making optical transducers, comprising: producing an integrated structure including, in a matrix array, a plurality of discrete light sources, a plurality of discrete light detectors each laterally spaced from a light source, a light shield in the space between a light source and a light detector for shielding the light detector from direct exposure to the light source, and a transparent plastic potting material embedding the light sources, light detectors and light shield; and cutting the integrated structure, along lines of the matrix, into individual optical units, each including a light source, a light detector, a light shield therebetween all embedded in the transparent plastic potting material, and an optical window for outputting light from the light source, and for transmitting to the light detector light reflected back from the light source.
Several embodiments of the invention are described below for purposes of example. In all the described preferred embodiments, the plurality of light sources and light detectors are arrayed in the integrated structure in a rectangular matrix of a plurality of rows along a first orthogonal axis, and a plurality of columns along a second orthogonal axis; the integrated structure being cut along both the orthogonal axes to produce the individual optical units.
In one preferred embodiment of the invention described below, the light sources and light detectors are provided on opposite faces of a common base member with each light detector on a face thereof being in axial alignment with a light source on the opposite face thereof. In this embodiment, the common base member is of light-transparent material and is provided on at least one of its faces with the light shield, in the form of a shielding layer of light-blocking material, before the common base member is provided with the light sources or light detectors. The shielding layer is preferably a light-reflecting coating.
According to further features in this described preferred embodiment, the plurality of light sources on one face of the common base member, and the plurality of light detectors on the opposite face of the common base member, are embedded in separate bodies of the transparent plastic potting material. These bodies are coated with a light-blocking material on all their exposed faces except for one face to serve as the optical window for the respective optical unit.
A further embodiment is described wherein the light sources are provided on one face of a first base member, and the light detectors are provided on one face of a second base member; the first and second base members being bonded together in a back-to-back relation, with the light shield inbetween, to produce the integrated structures. In this embodiment, the first and second base members are of transparent material, and at least one of the base members is provided with the light shield, in the form of a shielding layer of a light-blocking material, before being bonded to the other base member.
Further embodiments are described below wherein the light sources are provided on one face of a first base member and are embedded in one body of the transparent plastic potting material, and the light detectors are provided on one face of a second base member and are embedded in another body of the transparent plastic potting material. At least one of the bodies is provided with the light shield in the form of a shielding layer of a light-blocking material over the transparent plastic potting material. The two bodies of transparent plastic potting material are bonded together to produce the integrated structures with the shielding layer inbetween, and with each light source of the first base member aligned with a light detector of the second base member.
In one described embodiment, the light sources and light detectors are formed in a contiguous relation to each other on their respective base members, and the two base members are bonded together with the outer faces of their respective bodies of transparent plastic potting material in a face-to-face relation to each other, and with each light source of the first base member aligned with a light detector of the second base member in the transverse direction of the integrated structure.
In another described preferred embodiment, the light sources and light detectors are formed in a spaced relation to each other on their respective base members, and the two base members are bonded together with the outer faces of the respective bodies of transparent plastic potting material in a nested relation to each other, with each body of one base member received in a space of the other base member, and with each light source of the first base member aligned with a light detector of the second base member in the transverse direction of the integrated structure.
According to further aspects of the present invention there are provided optical transducers constructed in accordance with the foregoing method. As will be described more particularly below, the foregoing features not only permit the optical units of such transducers to be produced in volume and at lost cost, but also provide a very sturdy construction enabling them to withstand rough handling.
Further features and advantages of the invention will be apparent from the description below.